From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D6511226CEB; Thu, 24 Apr 2025 11:48:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745495330; cv=none; b=pgs1Iy5O6EAEQ7Thanom3dqxO8PBBIc6JWJJB+yYKlpwQSYnMC4gGWrG5LSyJWoZ+e7LVtYZrBtaVlQrQVpJw6Kg1HHs26pvkc2/bUzaMkCks1JXvJ9bYrSPkGHS8rOSS29uOIFCLI5aMv6mXnBuBEoZzr8v6UFXIRXDRfcugfw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745495330; c=relaxed/simple; bh=tka2nkFt+YTLCXeIlbWv0s0FI0+bvvfgH7BhTLKbgbc=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=j8NLuvH5tCKHHb9HWMNdbDdGfXQSvnyGqV4ELkA0+crREmSupZc2olQa89QsYVBIZxETTrFRbViriaNDYoVB0sU/kZSeEdUlXW/0h8fXWTkP6rcvpIRLgl37+VnaXRotpn5RQEdT4H31tZfrj62UIz/X10u75b/LKU182n6moB4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OpMEaFQg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OpMEaFQg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 93A79C4CEE3; Thu, 24 Apr 2025 11:48:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745495329; bh=tka2nkFt+YTLCXeIlbWv0s0FI0+bvvfgH7BhTLKbgbc=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=OpMEaFQgrsCFmilT9N52pKTAWjYXGjAEdUw/dslCJEHMH1dLN7+PoNQ+/AQKYGUy6 f06S3drR2+BXF+BR4zBZN2QeoihIq54646IotI75oaD1OMc9Oh5bJgoQcPV8QkHS84 Cp84P+Sqyp6M7LLc7LxRVtAl/GDvlVrz3kOtJKbqs41XtFmubfZ0Qj9uRYMx2W6pJB HFG+3+1EvQ4x3QSOZIGQo93bCesS7N1Cl7dJAMcpotmh+aXP6mUNVNt4VumEkYOirJ e2MSE5Ym5GJrTR/GbPdfvaKuy1D70lnu+Rapw93eKq28e/97AEuU37rNMYOQPPDGXG QGDu85Yezj58w== Message-ID: Subject: Re: [RFC][PATCH] saner calling conventions for ->d_automount() From: Jeff Layton To: Al Viro , linux-fsdevel@vger.kernel.org Cc: Christian Brauner , David Howells , linux-nfs@vger.kernel.org, Steven Rostedt , Miklos Szeredi , linux-cifs@vger.kernel.org Date: Thu, 24 Apr 2025 07:48:47 -0400 In-Reply-To: <20250424060845.GG2023217@ZenIV> References: <20250424060845.GG2023217@ZenIV> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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conventions for ->d_automount() instances have > an odd wart - returned new mount to be attached is expected to have > refcount 2. >=20 > That kludge is intended to make sure that mark_mounts_for_expiry() called > before we get around to attaching that new mount to the tree won't decide > to take it out. finish_automount() drops the extra reference after it's > done with attaching mount to the tree - or drops the reference twice in > case of error. ->d_automount() instances have rather counterintuitive > boilerplate in them. >=20 > There's a much simpler approach: have mark_mounts_for_expiry() skip the > mounts that are yet to be mounted. And to hell with grabbing/dropping > those extra references. Makes for simpler correctness analysis, at that.= .. > =20 > Signed-off-by: Al Viro > --- > diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesy= stems/porting.rst > index 767b2927c762..749637231773 100644 > --- a/Documentation/filesystems/porting.rst > +++ b/Documentation/filesystems/porting.rst > @@ -1203,3 +1203,10 @@ should use d_drop();d_splice_alias() and return th= e result of the latter. > If a positive dentry cannot be returned for some reason, in-kernel > clients such as cachefiles, nfsd, smb/server may not perform ideally but > will fail-safe. > + > +--- > + > +**mandatory** > + > +Calling conventions for ->d_automount() have changed; we should *not* gr= ab > +an extra reference to new mount - it should be returned with refcount 1. > diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystem= s/vfs.rst > index ae79c30b6c0c..cc0a58e96770 100644 > --- a/Documentation/filesystems/vfs.rst > +++ b/Documentation/filesystems/vfs.rst > @@ -1411,9 +1411,7 @@ defined: > =20 > If a vfsmount is returned, the caller will attempt to mount it > on the mountpoint and will remove the vfsmount from its > - expiration list in the case of failure. The vfsmount should be > - returned with 2 refs on it to prevent automatic expiration - the > - caller will clean up the additional ref. > + expiration list in the case of failure. > =20 > This function is only used if DCACHE_NEED_AUTOMOUNT is set on > the dentry. This is set by __d_instantiate() if S_AUTOMOUNT is > diff --git a/fs/afs/mntpt.c b/fs/afs/mntpt.c > index 45cee6534122..9434a5399f2b 100644 > --- a/fs/afs/mntpt.c > +++ b/fs/afs/mntpt.c > @@ -189,7 +189,6 @@ struct vfsmount *afs_d_automount(struct path *path) > if (IS_ERR(newmnt)) > return newmnt; > =20 > - mntget(newmnt); /* prevent immediate expiration */ > mnt_set_expiry(newmnt, &afs_vfsmounts); > queue_delayed_work(afs_wq, &afs_mntpt_expiry_timer, > afs_mntpt_expiry_timeout * HZ); > diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c > index 83ac192e7fdd..05d8584fd3b9 100644 > --- a/fs/fuse/dir.c > +++ b/fs/fuse/dir.c > @@ -319,9 +319,6 @@ static struct vfsmount *fuse_dentry_automount(struct = path *path) > =20 > /* Create the submount */ > mnt =3D fc_mount(fsc); > - if (!IS_ERR(mnt)) > - mntget(mnt); > - > put_fs_context(fsc); > return mnt; > } > diff --git a/fs/namespace.c b/fs/namespace.c > index bbda516444ff..1807ccb1a52d 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -3903,10 +3903,6 @@ int finish_automount(struct vfsmount *m, const str= uct path *path) > return PTR_ERR(m); > =20 > mnt =3D real_mount(m); > - /* The new mount record should have at least 2 refs to prevent it being > - * expired before we get a chance to add it > - */ > - BUG_ON(mnt_get_count(mnt) < 2); > =20 > if (m->mnt_sb =3D=3D path->mnt->mnt_sb && > m->mnt_root =3D=3D dentry) { > @@ -3939,7 +3935,6 @@ int finish_automount(struct vfsmount *m, const stru= ct path *path) > unlock_mount(mp); > if (unlikely(err)) > goto discard; > - mntput(m); > return 0; > =20 > discard_locked: > @@ -3953,7 +3948,6 @@ int finish_automount(struct vfsmount *m, const stru= ct path *path) > namespace_unlock(); > } > mntput(m); > - mntput(m); > return err; > } > =20 > @@ -3990,11 +3984,14 @@ void mark_mounts_for_expiry(struct list_head *mou= nts) > =20 > /* extract from the expiration list every vfsmount that matches the > * following criteria: > + * - already mounted > * - only referenced by its parent vfsmount > * - still marked for expiry (marked on the last call here; marks are > * cleared by mntput()) > */ > list_for_each_entry_safe(mnt, next, mounts, mnt_expire) { > + if (!is_mounted(&mnt->mnt)) > + continue; > if (!xchg(&mnt->mnt_expiry_mark, 1) || > propagate_mount_busy(mnt, 1)) > continue; > diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c > index 973aed9cc5fe..7f1ec9c67ff2 100644 > --- a/fs/nfs/namespace.c > +++ b/fs/nfs/namespace.c > @@ -195,7 +195,6 @@ struct vfsmount *nfs_d_automount(struct path *path) > if (IS_ERR(mnt)) > goto out_fc; > =20 > - mntget(mnt); /* prevent immediate expiration */ > if (timeout <=3D 0) > goto out_fc; > =20 > diff --git a/fs/smb/client/namespace.c b/fs/smb/client/namespace.c > index e3f9213131c4..778daf11f1db 100644 > --- a/fs/smb/client/namespace.c > +++ b/fs/smb/client/namespace.c > @@ -283,7 +283,6 @@ struct vfsmount *cifs_d_automount(struct path *path) > return newmnt; > } > =20 > - mntget(newmnt); /* prevent immediate expiration */ > mnt_set_expiry(newmnt, &cifs_automount_list); > schedule_delayed_work(&cifs_automount_task, > cifs_mountpoint_expiry_timeout); > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 8ddf6b17215c..fa488721019f 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -10085,8 +10085,6 @@ static struct vfsmount *trace_automount(struct de= ntry *mntpt, void *ingore) > put_filesystem(type); > if (IS_ERR(mnt)) > return NULL; > - mntget(mnt); > - > return mnt; > } > =20 >=20 Much cleaner: Reviewed-by: Jeff Layton